1. Field of the Invention
This invention relates to a versatile machine tool for executing milling-type cutting operations on the external surfaces and particularly within internal passageways of a workpiece to form a desired machined surface such as spines, keyways or like machined surfaces.
2. Description of the Prior Art
In the metal working industry, the machining operations on a workpiece frequently include secondary precision machining operations to form key-way slots, grooves, tapped holes, blinds and the like. When these secondary machining operations are required on the external surface of the workpiece, a milling type machine of a vertical or horizontal type is suitable to carry out the machining operation. However, when an internal surface defined by a cylindrical bore in the workpiece must be machined, the nature of the machining operation dictates that the use of particular machining operation such as broaching, shaping, right angle head milling or Electrical Discharge Machining methods. It is a common requirement to machine both internal and external surfaces on a workpiece whereby on the one hand external machining operations can be usually carried out very efficiently and economically, while on the other hand internal machining operations dictate that the workpiece must be transferred to an all together different machine tool which is not only time consuming but also adds to the machining costs. Moreover, it is virtually impossible to perfectly realign a previously machined surface in a setup operation for carrying out additional machining operations on that workpiece. Even after setup operations are completed to align a workpiece on a chosen machine tool, there remains a continuing problem associated with metal removal operations within an internal passageway of the workpiece because of a lack of working space. It is likely that problems will occur when performing internal machining operations in a cavity of a workpiece whereas when machining operations are carried out externally of the workpiece, the machining operations are generally trouble free.
It is common to use broaching machines for machining operations on an internal surface because of fast metal removal as well as machining operations on a stacked arrangement of workpieces. The high cost of the machining using the broaching tool can be justified only on a large quantity of parts for cost effectiveness. Moreover, the broaching machine uses a long shaft with several cutting edges ground to the shape necessary to perform the needed machining operations. The cutting edges are positioned so that each successive edge cuts deeper than the previous cutting edge. When the broach is pulled or pushed a necessary extent through the workpiece, the machining operation is complete. Broaching machines also consume unusually large amounts of horsepower because considerable energy is required to operate the broach in relation to the size cut and of the large number of cutting edges in simultaneous contact with the workpiece. A clearance must be made available at the end of the cut to allow dumping of chips. As a result, the workpiece is broached through a cavity from each of opposite sides. A broaching machine requires an inordinate amount of floor space to carry out the machining operations due to the nature of the broaching operation. For example, a broach having a length of eight feet may be necessary for supporting a sufficient number of cutting edges for machining to a desired depth commencing at the small end of the broach. As the broach is pulled through the workpiece, the entire broach must pass to the opposite end part of the workpiece requiring an operating space about the surrounding floor area of sixteen feet in length plus the length of the workpiece. The cost of the valuable floor space increases the cost of the broaching operation. Broaches also, because of their mode of operation, impart a great shock on the workpiece at the commencement of the broaching operation. The broaching tool must be made of less brittle materials such as high speed steel which limits the use of the broach for cutting operations with workpieces comprised of softer materials. Carbide materials for broaching materials are occasionally used but they are very expensive to manufacture and are easily broken. The flexibility for machining operation by broaching machines is non-existent particularly because the cutters are uniquely formed for a single cutting operation and must be varied for each cutting operation. Broaching machines therefore do not embody the versatility needed for the machining operation.
Shaping machines are similar to a broaching machine because of the common requirements for a clearance to allow clearing or dumping of chips away from the tool. A single tool usually comprises the cutter made of high speed steel which consumes unusually large amounts of energy in the form of horse power of the machine which needlessly exposes the machining operation to the disadvantage of shock loads. Repetitive cutting strokes must be executed until a desired depth of cut is reached. Like a broach, shaping machines can not execute blind cuts because of the need for the cutting tool to operate within a clearance at both ends of the stroke of cut so as to allow the entrance and exiting of the tool without interference. Although shaping tools are less expensive than broaches, the machining operation with a shaping tool is slower and fills the need for machining operations in instances when an exact size broach is not immediately available and the quantity of pieces requiring the machining operation are relatively small in number. The shaping tool like the broach requires a clearance at the end of a machining operation but the size of the clearance is less for a shaping tool.
Right angle milling machines have numerous problems. The end of the cutting head opposite the tool carrying end is usually of a larger more robust construction to help stabilize and support the cutting tool. Because of the cantilever relation of the cutting head, the cutting tool lacks stability and because of the head size, it can normally penetrate only short distances into cavities of a workpiece notwithstanding the tapered construction of the cutting head. The unavoidable deflection of the cutting head due to its cantilever construction precludes the use of carbide tooling which will break under deflections by the cutting head, thus necessitates the use of high speed steel materials to form the cutting tool which are of a limited size. The right angle milling head offers certain desirable benefits including the use of rotary type tools which are less expensive and provide the opportunity to cut a variety of widths, execute plunge cuts, start and stop cutting without clearance and the cutting path is used for chip disposal. An example of a known machine tool is disclosed in U.S. Pat. No. 4,400,859 which discloses a cantilever shaped cutter arm supported by a spindle head to present a tool in a right angle relation to the extended length of the cantilever arm. The entire cutter spindle head including drive motor is moved on a bed for positioning of a cutting tool along X and Z axes while the workpiece can be traversed independently of the cutting head for Y axis adjustment. Also the workpiece is mounted on a turn-table like sub-base which can rotate about an axis that is vertical and parallel with the X axis movement of the spindle head. The mass making up the spindle head including its drive and necessary utilities precludes machining deeply within the cavity of a workpiece.
An electrical discharge machine is useful for carrying out internal and external machining operations on a workpiece but is expensive and the machining operations are limited by the particular construction of the electrical discharge machine. In an electrical discharge machine using a stretched wire for the cutting operation, any surface of the workpiece that may contact the wire will be cut and therefore the cutting operation is limited to a single plane. An electro-type machine uses a probe burner and allows cutting through a bore to a partial extent, plunge cutting and cutting in any desired plane. The cutting action by these machines involves burning which can cause surface damage to the workpiece, which can not be tolerated in many instances.
It is an object of the present invention to provide a less expensive alternative for machining a workpiece than the types discussed hereinbefore.
It is another object of the present invention to provide a machine well suited for machining internal surfaces of a workpiece and at the same time may be utilized to execute machining operations on the external surfaces of the workpiece so as to alleviate the need for timely and sometimes complicated set-up operations heretofore required to execute such machining operations on a variety of different machine tools.